1. Field of the Invention
The present invention relates to detection of a remaining amount of developer in an image forming apparatus such as a laser printer, a copying machine, and a facsimile machine employing an electrophotographic method.
2. Description of the Related Art
In related-art image forming apparatuses, there are cases where a remaining amount of toner inside a toner container is detected using a piezoelectric sensor or an ultrasonic sensor.
For example, Japanese Patent Application Laid-Open No. 1-6986 discusses a remaining toner amount detection apparatus including a piezoelectric sensor. The piezoelectric sensor is disposed on the bottom of a hopper such that a detection unit is faced upward in a position where an agitator rotation thin plate member passes in proximity to the piezoelectric sensor. Such a detection apparatus detects a remaining toner amount based on the ratio of the time needed for an agitator to rotate one rotation to the time needed for pressure of the sensor to be detected. In this detection apparatus, an output of the piezoelectric sensor is fixed to the logic in the presence of toner where a remaining toner amount keeps a certain level of amount or more. On the other hand, an output of the piezoelectric sensor is fixed to the logic in the absence of toner where a toner amount decreases to a certain level of amount or less, and the amount is not detected.
The remaining toner amount detection unit disclosed in Japanese Patent Application Laid-Open No. 1-6986 can only detect the presence or absence of toner. Thus, the detection unit cannot sequentially detect changes in a remaining toner amount. Moreover, with the operation speed of image forming apparatuses accelerated recently, an agitation member operates at high speed. Thus, toner is stirred up and remains in a detection position of a piezoelectric sensor until the toner is completely used up. This causes a difficulty in providing a time period for which a remaining toner weight is not detected.